This invention relates to a plate lockup for a rotary cylinder of a printing press and, more particularly, to a plate lockup which embodies a lockup register for the leading end of the plate, a pair of deflectable lockup springs carried by the rotary cylinder, one for locking the trailing end of a plate and the other for clamping the leading end of a plate against the lead end register, and actuatable means for deflecting one spring to facilitate lockup of a trailing end of a plate and for deflecting the other spring into positive clamping position against a leading end of the same or a different plate.
The plate lockup of the present invention has been designed specifically for locking a photopolymer printing plate having a metallic or plastic substrate onto a plate cylinder of a flexographic printing press, but it has more general application for the lockup of plates to rotary cylinders of printing presses.
The present invention provides a relatively simple printing press plate lockup in which the leading end of the plate is maintained in proper register on the cylinder by a fixed lead end register and the lockup is achieved by first deflecting the trailing end lockup spring to engage the trailing end of a plate and then releasing it so that it will apply circumferential tension on the plate to pull the lead end of the plate against the lead end register and lock the plate firmly on the cylinder. The other lockup spring is then deflected for positively locking the lead end of the plate against the lead end register.
In a preferred embodiment, the deflections of both springs are controlled by an actuator interposed between the springs. The actuator is operated first to deflect one lockup spring for engagement with the trailing end of the plate and then to deflect the other spring and hold it in locking engagement with the leading end of the plate. The actuator is preferably a rotatable cam interposed between the springs which can be rotated in one direction to effect the trailing end lockup and then in the other direction to effect the lead end clamp. The cam is rotatable to an overcenter position with respect to the lead end clamping spring to maintain the spring in its clamping position until released by the reverse rotation of the cam.
The invention is adapted to provide a symmetrical lockup assembly so that the cylinder can rotate in either direction. The symmetrical lockup assembly includes a retainer for a pair of spaced-apart lead end lockup registers, means for mounting the pair of deflectable springs within the retainer intermediate the lead end lockup registers and means for supporting the common actuating means intermediate the springs. One of the lead end registers serves to lock up and register the lead end of the plate when the cylinder is rotating in one direction and the other lead end register serves to lock up and register the lead end of the plate when the cylinder is rotating in the opposite direction. The deflectable springs are symmetrically arranged so that their functions can be reversed depending on the direction of rotation of the cylinder.